Abstract: The effects of light intensity and nitrogen form on plant growth and the activities of H2O2-scavenging enzymes in leaves of tobacco were studied. The results showed that the plant growth was not affected by nitrogen form under liw light intensity, but considerably inhibited by ammonium nutrition under high light intensity. The chlorophyll contents of leaves were significantly increased by ammonium nutrition under low light intensity, however, the chlorophyll content per fresh weight was significantly decreased by ammonium nutrition under high light intensity. The MDA content was greatly increased by ammonium nutrition under high light intensity, but not significantly increased under low light intensity. The ascorbate content was considerably increased by increased light intensity, but significantly decreased by ammonium nutrition. The content of dehydroascorbate was greatly promoted by ammonium nutrition, especially under high light intensity.The activities of AsA-POD, MDAsA reductase, DA sA reductase and GSSG reductese were greatly increased by increased light intensity. Under high light intensity the activities of AsA- POD and GSSG reductase were greatly increased by ammonium nutrition, however, the activity of MDASA reductase was considerably inhibited.Under low light intensity the activities of AsA-POD and MDAsA reductase were significantiy increased by ammonium nutrition and the activity of GSSG reductase was not significantly increased. The activities of DASA reductase were increased by ammonium nutrition, but not significantly. There were no significant differences of activities of SOD and CAT among the treatments.